3.1.2 Starch, glycogen and cellulose

Question 1

Define polysaccharide, and describe how they are formed

Answer 1

Polysaccharides are polymers formed from the condensation of many monosaccharides.
Glycosidic bonds form between the monomers

Question 2

Describe the structure of starch

Answer 2

Starch is a polymer made up of 1-4 and 1-6 glycosidic bonds between the alpha glucose monomers

Question 3

Explain how the structure of starch relates to its function

Answer 3

• Starch is coiled, so it’s compact, therefore more alpha glucose monomers can be stored in little spaces
• Starch is highly branched, which gives it a large SA. This allows more enzymes to bind, and catalyse the hydrolysis of glycosidic bonds into alpha glucose, which is used during respiration
• Starch is insoluble, so it doesn’t affect the water potential
• Starch is large, so it cannot diffuse out the cell membrane

Question 4

Describe the structure of cellulose

Answer 4

• Cellulose is a polymer, which consists of many parallel, linear chains of B-glucose joined by 1-4 glycosidic bonds.
• Alternate B-glucose molecules are rotated through 180°.
• Hydrogen bonds form between the chains, forming bundles called microfibrils.

Question 5

Explain how the structure of cellulose
relates to its function

Answer 5

• Long and straight chains
• Become linked together by many hydrogen bonds to form fibrils
• Provide strength (to cell wall)

Question 6

Describe the structure of glycogen

Answer 6

• Glycogen is formed by the condensation of a-glucose, joined through 1-4 and 1-6 glycosidic bonds.

Question 7

Explain how the structure of glycogen
relates to its function

Answer 7

• Coiled so it’s compact, therefore more a-glucose can be stored in little spaces
• highly branched, which increases SA, so more enzymes can bind, catalyse the hydrolysis of glycosidic bonds, to form a-glucose, which is used during respiration
• insoluble, so it doesn’t affect the water potential

Question 8

Compare and contrast glycogen and starch

Answer 8

• Both are made from the elements C, H, O
• Both contain 1-4 and 1-6 glycosidic bonds
• Both are polymers of a-glucose
• Both are energy storage molecules
• Both are coiled so compact, large so they do no diffuse out of the cell, and insoluble
  so they do not affect the water potential
• Glycogen is found in animals, whereas starch is found in plants
• Glycogen is relatively more branched than starch. This is because animals have a higher demand for ATP than plants as they have higher metabolic rates therefore, the increased branching of glycogen increases the rate at which it can be hydrolysed into a-glucose, the substrate for respiration

Question 9

Compare and contrast starch and cellulose

Answer 9

• Both are made from the elements C, H, O
• Both are found in plants
• Cellulose only contains 1-4 glycosidic bonds, whereas starch contains both 1-4 and 1-6 glycosidic bonds
• Cellulose is a polymer of B-glucose, whereas starch is a polymer of a-glucose
• Cellulose is structural and found in cell walls, whereas starch is an energy storage molecule
• Cellulose is unbranched, whereas starch is branched
• Hydrogen bonds form between parallel strands in cellulose to form fibrils, but there are
  no fibrils within starch

Question 10

Compare and contrast glycogen and cellulose

Answer 10

• Both are made from the elements C, H, O
• Cellulose only contains 1-4 glycosidic bonds, whereas glycogen contains both 1-4 and 1-6 glycosidic bonds
• Cellulose is a polymer of B-glucose, whereas glycogen is a polymer of a-glucose
• Cellulose is structural and found in cell walls, glycogen is an energy storage molecule
• Cellulose is unbranched, whereas glycogen is branched
• Cellulose is found in plants whereas glycogen is found in animals
• Hydrogen bonds form between parallel strands in cellulose to form fibrils. There are no fibrils within glycogen

Question 11

Hemicellulose is a small molecule formed mainly from
five-carbon (pentose) sugar monomers. It acts as a cement
holding cellulose fibres together. Like hemicellulose,
lignin is a polymer, but it is not a carbohydrate. It covers the cellulose in the cell wall and supplies additional strength. Compare and contrast hemicellulose and cellulose

Answer 11

• Both are polymers/polysaccharides.
• Both contain glycosidic bonds.
• Both are made from the elements C, H and O.
• Hemicellulose is shorter than cellulose.
• Hemicellulose is made from pentose sugars whereas cellulose is made from glucose, which is a hexose sugar